Method for enhancing the three-dimensional effect of a raised plastic surface using in-mold labeling and the label used therewith

ABSTRACT

A method of enhancing the three-dimensional effect of a plastic part and the label used therewith is disclosed. A label for enhancing the three-dimensional visual effect which comprises a plastic core and/or, an insulating layer, and/or a heat-activated adhesive backing is disclosed. The label is aligned on the surface of a relieved mold. When plastic is forced against the back surface of the label, the label is stretched and forced into the relief along with the plastic. The label adheres to the plastic part by either a heat-activated adhesive backing or the core forms a melts/weld interface with the molded part creating a permanent bond between the label and the molded part.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for enhancing thevisual effect of a three-dimensional molded part using in-mold labelingand the label used therewith, particularly a method and label forenhancing the three-dimensional visual effect of raised surfaces on ablow molded article.

BACKGROUND OF THE INVENTION

[0002] It is well known to apply conventional paper and plastic filmlabels to two-dimensional surfaces of blow molded plastic articles, suchas shampoo bottles and beverage containers, after the part has beenremoved from the mold. To improve the efficiency of blow moldingoperations, transfer machines were developed which place labels on theblow mold itself before the plastic part is formed. When the plasticarticle is blow molded, the label either melts or adheres to thetwo-dimensional container surface.

[0003] U.S. Pat. No. 5,266,377, issued to Kinoshita et al., discloses alabel and method for applying a label during in-mold molding. The labelcomprises a printed layer formed on a surface of a non-oriented plasticbased film over which a membrane layer is overlapped. The label isinserted into a mold for in-mold labeling and is held in the properposition on the mold using vacuum suction or static electricity. Plasticis then injected into the mold and the membrane layer on the label bondsto the plastic article.

[0004] U.S. Pat. No. 5,223,315, issued to Katsura et al., discloses alabel for two-dimensional surfaces consisting of a base of stretchedfilm having a thermal shrinkage ratio greater than the mold shrinkageratio of a plastic constituting the outer surface of a container. Usingmaterials that satisfy these ratios prevents creasing and swelling ofthe label on containers with polyolefin outer surfaces.

[0005] U.S. Pat. No. 5,256,365, issued to Gordon et al., discloses amethod of placing a label on mold cavities in a blow molding machineusing an in-mold labeling system including first and second magazineswith rotary members and vacuum assist.

[0006] U.S. Pat. No. 5,639,536, issued to Yamazaki et al., discloses themethod of applying a transfer layer having projections and recessesfiner than those on a molded part to produce a matte surface with goodwear characteristics. The recesses on the molded part are up toapproximately 300 microns deep and present therefore, essentially atwo-dimensional surface.

[0007] The above-mentioned patents work satisfactorily for moldedarticles with thin walls, such as two-liter plastic beverage bottles andshampoo containers having wall thicknesses of approximately 0.015 to0.060 inches. These articles retain relatively little heat in the wallscompared to thick-walled molded articles, such as cases for power tools,which typically have wall thicknesses of approximately 0.055 to 0.250inches. Thick-walled articles require a different label capable ofwithstanding the increased heat retained and subsequently released fromthe thick-walled sections. Moreover, the above-described background artis generally limited only to a two-dimensional surface and does notenhance the appearance of three-dimensional surfaces.

[0008] What is desired, therefore, is a label for in-mold labeling ofplastic parts which is capable of being in a mold cavity thereforetaking on the three-dimensional appearance of the relieved features orthe entire molded product, and which is capable of being used in in-moldlabeling operations on thick-walled molded parts which retain asubstantial amount of heat in the thick walls. In another aspect, whatis desired is a method of enhancing the three-dimensional appearance ofa raised surface on a plastic part using an in-mold label.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of this invention to provide a labelfor in-mold labeling of plastic parts that is capable of being in a moldcavity therefore taking on the three-dimensional appearance of therelieved features or the entire molded product.

[0010] Another object of this invention is to provide a label which iscapable of being used in in-mold labeling operations on thick-walledmolded parts which retain a substantial amount of heat in the thickwalls.

[0011] Yet another object of this invention is to describe a method ofenhancing the three-dimensional appearance of a raised surface on aplastic part using an in-mold label.

[0012] In one embodiment of the present invention, the label itselfcomprises a printed plastic, such as polypropylene or polyethylene,having a background and lettering and/or one or more patterns such asphoto graphics, a heat-activated adhesive layer on the bottom surfacethereof for adhering to the molded article, and a surface layer, such asvarnish, on the top surface to insulate the core from the cool moldcavity and/or protect the printed core from damage.

[0013] To apply the label, the label first must be positioned on themold surface using a transfer system, mechanical tooling components, orby hand. The label is precisely held in place on the mold surface byvacuum suction and/or static electricity. A parison, the semi-solid,molten, plastic “tube” that is extruded from the blow molding machine,is dropped between the mold halves. The mold then closes around theparison and air is injected into the parison forcing the parison to takethe shape of the mold cavity, i.e., the finished molded part, includingany relief cut into the mold cavity. The label is also forced to stretchand take the shape of the cavity relief or part contour by the plasticparison resulting in an enhanced three-dimensional visual effect of theraised article surface. The heat from the parison causes theheat-activated adhesive layer to bond to the molded part.

[0014] In another embodiment, the label comprises a plastic core, suchas polyethylene or polypropylene, and a surface layer, such as a varnishcoating. In this embodiment, when the plastic parison is blown andcontacts the label, the heat from the plastic causes the bottom surfaceof the plastic core to melt and permanently bond to the parison.

[0015] The invention and its particular features and advantages willbecome more apparent from the following detailed description consideredwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a cross sectional view of a label in accordance withthe present invention;

[0017] FIG. 2 is a plan view of the label of FIG. 1 showing thelettering which may be raised to produce a three dimensional effect;

[0018] FIG. 3a is a perspective view of one mold cavity used to producethe label of FIG. 1 illustrating the cavity relief; and

[0019] FIG. 3b is a perspective view of a molded part manufactured fromthe mold cavity illustrated in FIG. 3a.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention is described as applying to a blow moldingprocess. However, this invention is not limited to blow molding and canbe used with any other plastic forming process in which the plastic partis formed into a three-dimensional surface such as injection molding. Inblow molding, a parison, the semisolid, molten, plastic “tube”, isproduced by extruding heated plastic through a die or an annular ringand pin set. A blow mold, having at least two cavities or a cavity andcore set, closes around the parison. Relief is cut into the mold tocreate raised surfaces on the molded part. Pressurized gas is theninjected into the interior of the parison which is forced to conform tothe shape of the mold cavities including any contours or relief cut intothe mold causing the molded part to have a raised surface. Coolant isgenerally fed through bores in the mold to cool the mold thereforereducing the time it takes for the molded part to become self-supportingand thus removable from the mold. However, certain engineering plasticsrequire a heated mold to properly form a part and thus the mold maycontain heaters or have hot water or oil piped through the mold.

[0021] Referring first to FIG. 1, label 1 generally comprises a printed,flexible substrate 3 made from a plastic such as polypropylene orpolyethylene. The specific core polymer is not critical as long as it iscapable of stretching sufficiently to cover the relief and/or contour.Preferably, the core material will be compatible with the material ofthe molded part to take advantage of melt/weld properties of compatiblematerials and/or for recycling requirements. For example, apolypropylene or a polypropylene blend core would be compatible with apolypropylene part although a polyethylene core would also melt/weld toa polypropylene part. In a preferred embodiment, core 3 is approximately0.004 inches thick. However, core 3 may range from at least 0.002 inchesto 0.14 inches thick. The core thickness, as well as the overall labelthickness, is dependent on factors such as material stretchability andthe depth of the cavity relief. For example, thicker labels of a moreelastic material work best with deeply relieved parts. Label 1 has beenused on relief that is less than 0.005 inches deep to 0.125 inches deepdepending on the limitations of the substrate. The core thickness can berelatively thin if surface layer 2 is fairly thick, i.e., at least 0.002inches.

[0022] A heat-activated adhesive layer 4 covers the bottom surface ofcore 3 to assist the melt/weld adhesion of the label to the moldedarticle. In a preferred embodiment, adhesive layer 4 is either sprayedor rolled on during the printing process, although other known means maybe used. When adhesive layer 4 is used, the core material may or may notactually bond to the part. Therefore, any type of label, such as afoil-type label, may be used having material that is very dissimilar tothat of the molded part.

[0023] A surface layer 2 covers the top surface of label 1. In apreferred embodiment, surface layer 2 is a varnish coating, however, anover-laminate such as polypropylene may also be used. Surface layer 2insulates core 3 from the relatively cold mold surface allowing themolded article and core 3 to remain at elevated temperatures longer tobetter melt and bond to the surface of the part. Core 3 is more likelyto melt and bond to the plastic part if core 3 is thin and insulatinglayer 2 is thick. Surface layer 2 is not generally necessary forinsulating purposes if adhesive layer 4 is used to attach the labelrather than melt welding. However, in all circumstances, surface layer 2provides scuff protection to printed core 3. Surface layer 2 may bepermanently bonded to core 3 and remain as part as the label or may be atemporary, readily-strippable connection that is peeled off the label ata point after the molded part is removed from the mold.

[0024] The above-mentioned thicknesses are used to apply the label tothick-walled parts which retain more heat in the walls than thin-walledparts. Present thin labels used on thin-walled parts may distort whensubjected to heat contained in thick-walled parts.

[0025] In another embodiment, adhesive layer 4 is not used. Label 1adheres to the molded article by a melt/weld interface between core 3and the molded article. In this case, it is important that the corematerial is compatible with the molded part material since there is noadhesive to aid the adherence of label 1 to the molded part. Dissimilarlabels, such as nylon and polyethylene, have different melt temperatureswhich make it very difficult to form an effective melt/weld interfaceand therefore generally require adhesive layer 4.

[0026] Referring now to FIG. 2, printed label 1 may comprise abackground 6 and pattern 7, lettering 5, and/or photo graphics which maybe of the same or different color as the background. The pattern orlettering that will be raised may be shadowed in different colors tocreate a multi-colored raised wall on the finished part. In theillustrated label, lettering 5 is designed to conform to the raisedarticle surface and is of a different color to produce a more dramaticthree-dimensional effect when label 1 is bonded to the finish part. Anypart of label 1 may be raised.

[0027] As shown in FIG. 3a, cavity 15 of a blow molding tool havingcavity mold part surface 20 also has cavity relief 10 further cut intothe cavity surface 20 such that in the molded part 16, relief 11 standsout from the part surface 21 (as shown in FIG. 3b).

[0028] To enhance the three-dimensional effect, label 1 is placed onmold cavity 15 with the top surface of label 1 contacting cavity surface20 by a transfer machine, such as a robotic arm, of the type well knownin the industry and typically held in place by either a vacuum and/orstatic electricity. Label 1 must be positioned such that lettering 5 orpattern 7, which is desired to be raised, is properly aligned withcavity relief 10.

[0029] Once label 1 is positioned and the parison drops, the blow moldthen closes around the parison. The parison is then blown and theplastic takes the form of the mold including filling in any cavityrelief 10. This results in label 1 being stretched and forced to takethe shape of the cavity relief 10 causing label 1 to becomethree-dimensional.

[0030] For thick-walled parts, it may be advantageous to use a separateheated plate in the label area of the mold cavity to subject the labelto a higher temperature to better ensure a proper weld/melt interfacebetween label 1 and the molded part. Of course, a heated plate may notbe necessary if an adhesive layer is used. Thin-walled parts generallydo not require a separate heated plate.

[0031] The present invention, therefore, provides a label for in-moldlabeling of plastic parts which is capable of being in a mold cavitytherefore taking on the three-dimensional appearance of the relievedfeatures or the entire molded product, and which is capable of beingused in in-mold labeling operations on thick-walled molded parts whichretain a substantial amount of heat in the thick walls. In anotheraspect, the present invention provides a method of enhancing thethree-dimensional appearance of a raised surface on a plastic part usingan in-mold label.

[0032] Although the present invention has been described in reference toa thick-walled structure, the above-described invention works equallywell with thin-walled structures.

[0033] Although the invention has been described with reference to aparticular arrangement of parts, features and the like, these are notintended to exhaust all possible arrangements or features, and indeedmany other modifications and variations will be ascertainable to thoseof skill in the art.

What is claimed is:
 1. An in-mold label for enhancing the visual effectof a three-dimensional molded part having a three-dimensional partsurface, the label comprising: a flexible substrate layer adapted tostretch and assume the shape of the part surface during molding, saidflexible substrate layer having a first surface and a second surface; aheat-activated adhesive layer applied to the first surface of saidflexible substrate layer; and wherein said heat-activated adhesive layeradheres said flexible substrate layer to the part surface duringmolding.
 2. The in-mold label of claim 1 further comprising a protectivelayer attached to the second surface of said flexible substrate layer toprovide scuff protection to said flexible substrate layer.
 3. Thein-mold label of claim 2 wherein said protective layer is formed from aninsulating material to insulate said flexible substrate layer and saidheat-activated adhesive layer from a mold used to form the molded part,thereby allowing the molded part, said flexible substrate layer and saidheat-activated adhesive layer to remain at an elevated temperaturelonger to better bond the label to the molded part.
 4. The in-mold labelof claim 1 wherein said flexible substrate layer is formed from athermo-plastic material which is chemically compatible with the partsurface so that, in addition to said heat-activated adhesive layeradhering said flexible substrate layer to the part surface, saidflexible substrate layer welds to the three-dimensional part surfaceduring molding.
 5. The in-mold label of claim 4 wherein said flexiblesubstrate layer is formed from polypropylene.
 6. The in-mold label ofclaim 4 wherein said flexible substrate layer is formed frompolyethylene.
 7. An in-mold label for enhancing the visual effect of athree-dimensional molded part having a three-dimensional part surface,the label comprising: a flexible substrate layer adapted to stretch andassume the shape of the part surface during molding, said flexiblesubstrate layer having a first surface and a second surface; and whereinsaid flexible substrate layer is formed from a thermo-plastic materialwhich is chemically compatible with the part surface so that the firstsurface of said flexible substrate layer welds to the part surfaceduring molding.
 8. The in-mold label of claim 7 further comprising aprotective layer attached to the second surface of said flexiblesubstrate layer to provide scuff protection to said flexible substratelayer.
 9. The in-mold label of claim 8 wherein said protective layer isformed from an insulating material to insulate said flexible substratelayer from a mold used to form the molded part, thereby allowing themolded part and said flexible substrate layer to remain at an elevatedtemperature longer to better bond the label to the molded part.
 10. Thein-mold label of claim 7 wherein said flexible substrate layer is formedfrom polypropylene.
 11. The in-mold label of claim 7 wherein saidflexible substrate layer is formed from polyethylene.
 12. The in-moldlabel of claim 7 further comprising a heat-activated adhesive layerapplied to the first surface of said flexible substrate layer to adheresaid flexible substrate layer to the part surface during molding,thereby enhancing the bond between said flexible substrate layer and thepart surface.
 13. A molded article comprising: at least one molded parthaving a three-dimensional part surface; and a label comrpising: aflexible substrate layer adapted to stretch and assume the shape of thepart surface during molding, said flexible substrate layer having afirst surface and a second surface; a heat-activated adhesive layerapplied to the first surface of said flexible substrate layer; andwherein said heat-activated adhesive layer adheres said flexiblesubstrate layer to the part surface during molding.
 14. The moldedarticle of claim 13 wherein said label further comprises a protectivelayer attached to the second surface of said flexible substrate layer toprovide scuff protection to said flexible substrate layer.
 15. Themolded article of claim 14 wherein said protective layer is formed froman insulating material to insulate said flexible substrate layer andsaid heat-activated adhesive layer from a mold used to form the moldedpart, thereby allowing the molded part, said flexible substrate layerand said heat-activated adhesive layer to remain at an elevatedtemperature longer to better bond the label to the molded part.
 16. Themolded article of claim 13 wherein said flexible substrate layer isformed from a thermo-plastic material which is chemically compatiblewith the part surface so that, in addition to said heat-activatedadhesive layer adhering said flexible substrate layer to the partsurface, said flexible substrate layer welds to the three-dimensionalpart surface during molding
 17. A molded article comprising: at leastone molded part having a three-dimensional part surface; and a labelcomrpising: a flexible substrate layer adapted to stretch and assume theshape of the part surface during molding, said flexible substrate layerhaving a first surface and a second surface; and wherein said flexiblesubstrate layer is formed from a thermo-plastic material which ischemically compatible with the part surface so that the first surface ofsaid flexible substrate layer welds to the part surface during molding.18. The molded article of claim 17 wherein said label further comprisesa protective layer attached to the second surface of said flexiblesubstrate layer to provide scuff protection to said flexible substratelayer.
 19. The molded article of claim 18 wherein said protective layeris formed from an insulating material to insulate said flexiblesubstrate layer from a mold used to form the molded part, therebyallowing the molded part and said flexible substrate layer to remain atan elevated temperature longer to better bond the label to the moldedpart.
 20. The molded article of claim 17 wherein said label furthercomprises a heat-activated adhesive layer applied to the first surfaceof said flexible substrate layer to adhere said flexible substrate layerto the part surface during molding, thereby enhancing the bond betweensaid flexible substrate layer and the part surface
 21. An method ofmolding an article and enhancing the visual effect of athree-dimensional part surface thereof comprising the steps of:providing a label having a flexible substrate layer adapted to stretchand assume the shape of the part surface during molding, the flexiblesubstrate layer having a first surface and a second surface; positioningthe label in a mold cavity and maintaining its position therein; andforming the plastic part in the mold cavity and stretching the label toassume the shape of the part surface.
 22. The method of claim 21 whereinsaid forming step comprises blow molding the plastic part in the moldcavity and stretching the label to assume the shape of the part surface23. The method of claim 21 wherein the flexible substrate layer of thelabel is formed from a thermo-plastic material which is chemicallycompatible with the part surface, and further comprising the step ofwelding the first surface of the flexible substrate layer to the partsurface during molding.
 24. The method of claim 21 wherein the labelincludes a heat-activated adhesive layer applied to the first surface ofthe flexible substrate layer, and further comprising the step ofadhering the flexible substrate layer to the part surface during moldingby way of the heat-activated adhesive layer.
 25. The method of claim 21wherein said positioning step is accomplished by using a robotic arm.26. The method of claim 21 wherein said maintaining step is accomplishedby using vacuum suction.
 27. The method of claim 21 wherein saidmaintaining step is accomplished by using static electricity.